Piston slap

[swimmingcap]

Is it common, as I have a bad rattle when i pull away, but goes if you ease the twist grip off a little then power through it, the performance is good and I can drive it without the rattle, but i have to keep ridding the throttle, any help would be good, before i take the barrel off, I thought it might be pinking, but have changed to a 9 series plug, I have only just got the bike, so I can't compare it to before and after.

[eddie666]

if its gets better with the power on and sounds worse when its closed throttle, it could be piston slap

i dont know if you would of noticed this: run untill the bike is hot ( warmed up normal temp ) then you stop for 10 - 15 mins ( switch it off ) then get on it and get going , IF IT FEELS FASTER for the first few minutes, ( poping wheeles in 1st and 2nd gears ) from starting off is a good way off feeling the power, then ride it for a bit longer then try it again with out switching it off, if you feel its loseing power then it may need a top end rebuild,

put a screw driver handle to your ear and put the other end on the barlel and rev up the bike and listen for the tapping, you should hear it if its in there,

how many miles has it done ?
is it using a lot of oil ?

is the noise always there but gets louder when you swith off the throttle ?

mine is ready for a top end rebuild , it sounds like a tin full of nuts & bolts rattling in the engine , gets better the more you power it,

[swimmingcap]

Thanks for the info, I chickened out as I was coming back to UK and popped the barrel off as its only held on with 4 nuts, took barrel to local reborers and they said it was not to bad, but worn a little at top end and the piston showed some blow by, so will let you know if it fix's the noise, apart from that all is normal, only clocked 11,000 KMS so maybe I am being a bit early in rebuilding top end, but will let you know if the noise goes. The bike runs well the more power you apply,

[swimmingcap]

Still got the noise after rebore, it only seems to be there when bike is ridden, can not do it with screwdriver, as I might fall off trying to do this method whilst ridding, I am thinking of checking the power valve in the barrel, to see if i can detect any excessive movement , the problem is the bike is in Thailand so can't compare it to another, I am near Gatwick airport so i cna only do one job at a time with each visit, I am thinking the wear on balance shaft bearing would be a wine not a rattle, the bike runs fine and is fun to use, but would be interested if anyone near me, we could meet up and I could try there bike, ????

[fallenmikethebike]

[quote="swimmingcap" it only seems to be there when bike is ridden, can not do it with screwdriver, as I might fall off trying to do this method whilst ridding.
PMSL, FFS,ain't you got any earphones? , sounds like the power bands gone south
Absolute classic, encore.
Mike

[knackeredMk1]

All CRMs make different noises.

My Mk1 with one barrel makes a different noise to another. The Mk3 I have just rebuilt is different again.

Unless the noise is permanent and disturbing my advice would be to leave alone and ride it.

[Bultacobob]

I know this is an old thread, but I have just bought a MK3 and it does exactly the same thing. Playing with the throttle makes the rattle go away for a while. Did you ever find a cure or the cause of the fault. I was ready to go down the top end rebuild but the bike has only done 7600 KMs and it all looks pretty good inside. I have rebuilt 2T in the past and never cured the rattles so reckon on just living with it.

[fallenmikethebike]

^^^^ Have you tried a compression test?
Mike

[Bultacobob]

Hi Mike, no, but I will, what should my reading be in PSI if Poss. Do you think that a random rattling that can be made to disappear with a bit of throttle play could be piston slap? It only happens on higher RPM and then only on acceleration. Playing in the dirt the engine is absolutely fine, but get it on the road and strange rattlings happen!!! I have rebuilt older 2T,s with odd sounds and yes you guessed, the noises never diapered and the engines went on forever. But the new bike has got me a bit paranoid, some people have had similar noises and no change on full engine rebuilds which I why I am a bit hesitant to start changing things. Still like you say a compression test seem like a good place to start.

Cheers
Rob

P.S took the bike out for its first shakedown ride after checking everything was tight and changing to silicone hoses. Was very impressed, it pulled like a four stroke at low revs and even had decent engine braking on steep hills. running at 13-45 is a bit noisy after 50mph, but seeing how well the bike pulls I think it will take 14-45 as a nice compromise.

[rich1960]

13/45 is the ideal compromise, 14/45 tends to run away with you on the tight nadgery stuff....but each to their own.

[helisupp]

I think a 14 tooth front sprocket is really just for the road, 13 tooth is ideal off road, easier on the clutch and it gives a bit more clearance for mud build up etc. 45 rear sprocket is spot on as per Bultacobob above.

[fallenmikethebike]

IMHO, if the readings get to just around 150 psi, all should be well. If it's much below this, some stripping down is required,as is also the case if it's significantly higher than this, but for the reason that the powervalve is probably gummed up.
The Honda p/valve system seemsto lend itself to ratling more than some other systems on the market, so don't fret overly about mechanical noise, just check the valves moving freely.
I run 14/45, mainly due to the amount of road work we have to do in this area to reach the Byways and also that our lanes tend towards the namby pamby side of "off roading", with some even having neatly mowed verges.
Mike

[Bultacobob]

Thanks for the info Mike, I did a lot of searching for the comp PSI and got nada, might be worth putting it in the FAQ's. I take your point on the gearing, For me the road work is about 50% but the trails are pretty gnarly in my opinion with steep rock and chalk inclines and descents. so will stick with 13 -45, however I noticed that the chain was just touching the plate the holds the front sprocket on and has worn the edge off slightly where as the 14 keeps it clear, So in am going to swap to 14-48 on the next change over, this will take the pressure off the sprocket bearing, rides the chain a bit higher so it does not contact the swing arm so much and will improve chain life. I will also extend the rear block to accommodate the larger rear sprocket. All this after the engine checks out !!!

[gregorious77]

I run 13/52 on my AR!!!
Also have a pinking type rattle at certain throttle position and revs but not worried about it at all its just the nature of the beast.
I have had a failed balancer shaft bearing which was a whine and since replacing the knock is still there but like I said only certain TP and revs.
Just ride it and change the oil regularly.

[Bultacobob]

Hi, Have done compression test it is about 170psi is that OK Mike or to high? The prower vale seems OK and is moving freely. The bike has only done 4000 miles the cylinder and piston look pretty good, no marks, score lines etc.